O2 sensor on a 1994 toyota tercel

If you look straight at your engine. In front will your exhaust manifold. Right across from it on your radiator and grill will be your O2 sensor . It clipped to the frame with two sets of wires coming out of each side. That is your O2 sensor.

Usually the O2 sensor will be on the exhaust manifold close to the engine, I'm going to assume you have a pretty good idea of what you are doing so if you need more details don't hesitate to ask.